The most important factors predisposing to DVT are immobility of the extremity and the presence of a hypercoagulable condition. Immobility involves a lack of movement of the leg(s) for prolonged periods of time. With the lack of movement, the calf muscles do not contract and the blood in a lower leg does not get pushed out of the calf. The lack of blood movement, referred to as stasis, allows clots to form in the stagnant blood. When a patient is hypercoagulable, their blood is even more likely to clot. Typical causes of immobility are: 1) surgeries (particularly orthopedic, pelvic, abdominal, or neurological) with postoperative bedrest or limited limb mobility for days or longer; 2) major trauma with inability to get out of bed or move the limbs; 3) severe illness causing inability to get out of bed; 4) casts or immobilizing boots after surgeries or trauma; and, 5) travel on long trips involving sitting (e.g., in an airplane seat or car) for hours without getting up and walking around. Hypercoagulable conditions are caused by blood abnormalities affecting the clotting cascade, elevated platelets, malignancy, and the use of birth control pills or other medications—any of which may cause thrombosis.
Risk Factors for Deep Venous Thrombosis medical expert witness specialties include vascular surgery.